Abstract:

Data multiplexing subcarrier identification signal generating means
generates a data multiplexing subcarrier identification signal that
identifies subcarriers with which data signals are to be multiplexed.
Transmission signal generating means generates transmission signals by
multiplexing data signals with subcarriers according to the data
multiplexing subcarrier identification signal. Peak reducing transmission
signal generating means generates peak reducing transmission signals by
reducing peak power of the transmission signals according to peak
reducing signals in a combination of a first peak reducing process in
which subcarriers with which the data signals are not multiplexed are
used for the peak reducing signals and subcarriers with which the data
signals are multiplexed are not used for the peak reducing signals, and a
second peak reducing process in which both subcarriers with which the
data signals are not multiplexed and the subcarriers with which the data
signals are multiplexed are used for the peak reducing signals.

Claims:

1. A transmission signal generating apparatus for generating transmission
signals with reduced peak power, comprising:a data multiplexing
subcarrier identification signal generator that generates a data
multiplexing subcarrier identification signal that identifies subcarriers
with which data signals are to be multiplexed;a transmission signal
generator that generates transmission signals by multiplexing data
signals with subcarriers according to the data multiplexing subcarrier
identification signal generated by said data multiplexing subcarrier
identification signal generator; anda peak reducing transmission signal
generator that generates peak reducing transmission signals by reducing
peak power of said transmission signals generated by said transmission
signal generator according to peak reducing signals in a combination of a
first peak reducing process in which subcarriers with which the data
signals are not multiplexed are used for the peak reducing signals and
subcarriers with which the data signals are multiplexed are not used for
the peak reducing signals based on said data multiplexing subcarrier
identification signal, and a second peak reducing process in which both
subcarriers with which the data signals are not multiplexed and the
subcarriers with which the data signals are multiplexed are used for the
peak reducing signals.

2. The transmission signal generating apparatus according to claim 1,
wherein said peak reducing transmission signal generator means carries
out said second peak reducing process after having carried out said first
peak reducing process.

3. The transmission signal generating apparatus according to claim 2,
wherein said peak reducing transmission signal generator:recursively
repeats said first peak reducing process to generate the peak reducing
signals based on said transmission signals and adds the peak reducing
signals to said transmission signals by a predetermined number of times;
andthereafter, recursively repeats said second peak reducing process to
generate the peak reducing signals based on said transmission signals and
adds the peak reducing signals to said transmission signals by a
predetermined number of times.

4. The transmission signal generating apparatus according to claim 2,
wherein said peak reducing transmission signal generator
means:recursively repeats said first peak reducing process to generate
the peak reducing signals based on said transmission signals and adds the
peak reducing signals to said transmission signals until the peak power
of said transmission signals becomes smaller than a first threshold
value; andthereafter, recursively repeats said second peak reducing
process to generate the peak reducing signals based on said transmission
signals and adds the peak reducing signals to said transmission signals
until the peak power of said transmission signals becomes smaller than a
second threshold value which is smaller than said first threshold value.

5. The transmission signal generating apparatus according to claim 4,
wherein said peak reducing transmission signal generator:predetermines
upper limits respectively for the number of times that said first peak
reducing process is repeated and the number of times that said second
peak reducing process is repeated;shifts into said second peak reducing
process even if the peak power of said transmission signals is not
smaller than said first threshold value when the number of times that
said first peak reducing process is repeated reaches the upper limit
therefor; andoutputs said transmission signals as said peak reducing
transmission signals even if the peak power of said transmission signals
is not smaller than said second threshold value when the number of times
that said first peak reducing process is repeated reaches the upper limit
therefor.

6. The transmission signal generating apparatus according to claim 1,
wherein said peak reducing transmission signal generator does not use
subcarriers for which a modulation accuracy for the data signals is
required to be higher than a predetermined level in said second peak
reducing process, among the subcarriers with which the data signals are
multiplexed, for said peak reducing signals.

7. The transmission signal generating apparatus according to claim 6,
wherein said peak reducing transmission signal generator does not use
subcarriers for which a modulation multilevel number for the data signals
is equal to or higher than a predetermined level in said second peak
reducing process, among the subcarriers with which the data signals are
multiplexed, for said peak reducing signals.

8. A transmission signal generating method of generating transmission
signals with reduced peak power, comprising:generating a data
multiplexing subcarrier identification signal that identifies subcarriers
with which data signals are to be multiplexed;generating transmission
signals by multiplexing data signals with subcarriers according to the
data multiplexing subcarrier identification signal; andgenerating peak
reducing transmission signals by reducing peak power of said transmission
signals according to peak reducing signals in a combination of a first
peak reducing process in which subcarriers with which the data signals
are not multiplexed are used for the peak reducing signals and
subcarriers with which the data signals are multiplexed are not used for
the peak reducing signals based on said data multiplexing subcarrier
identification signal, and a second peak reducing process in which both
subcarriers with which the data signals are not multiplexed and the
subcarriers with which the data signals are multiplexed are used for the
peak reducing signals.

9. The transmission signal generating method according to claim 8, wherein
said second peak reducing process is carried out after said first peak
reducing process has been carried out.

10. A computer-readable medium containing a computer program for
controlling a transmission signal generating apparatus to generate
transmission signals with reduced peak power, said computer program
comprising:a sequence to generate a data multiplexing subcarrier
identification signal that identifies subcarriers with which data signals
are to be multiplexed;a sequence to generate transmission signals by
multiplexing data signals with subcarriers according to the data
multiplexing subcarrier identification signal; anda sequence to generate
peak reducing transmission signals by reducing peak power of said
transmission signals according to peak reducing signals in a combination
of a first peak reducing process in which subcarriers with which the data
signals are not multiplexed are used for the peak reducing signals and
subcarriers with which the data signals are multiplexed are not used for
the peak reducing signals based on said data multiplexing subcarrier
identification signal, and a second peak reducing process in which both
subcarriers with which the data signals are not multiplexed and the
subcarriers with which the data signals are multiplexed are used for the
peak reducing signals.

11. The computer-readable medium according to claim 10, wherein said
second peak reducing process is carried out after said first peak
reducing process has been carried out.

Description:

[0002]In recent years, attention has been drawn to OFDM (Orthogonal
Frequency Division Multiplexing). The OFDM has such features that the
receiver has a relatively simple circuit arrangement, the propagation
path can be regarded as flat in terms of subcarriers, and it can easily
be expanded into MIMO (Multiple Input Multiple Output).

[0003]According to the OFDM, since a plurality of carriers are multiplexed
in time domain, the signal power exhibits a high peak when the carriers
are brought into phase with each other in time domain. The high peak
leads to an increase in PAPR (Peak to Average Power Ratio). As the
increased PAPR reduces the coverage of the base station and increases the
power consumption, there has been a need for reducing the PAPR.

[0005]According to the TR with RT process, a subcarrier for a peak
reducing signal is provided in addition to a subcarrier for a data
signal, and a peak reducing signal for reducing peak power is generated
in the subcarrier for a peak reducing signal. The peak reducing signal is
added to the data signal, thereby reducing the peak power.

[0006]According to the TR without RT process, a peak reducing signal is
generated in the same band as a data signal and with sufficiently low
power compared with the data signal, and is added to the data signal,
thereby reducing the peak power.

[0007]The TR with RT process has such features that it can reduce the PAPR
without lowering the modulation accuracy (highering EVM) though the
spectrum use efficiency is lowered as the reduction in the PAPR
increases. The TR without RT process has such features that the spectrum
use efficiency is not lowered though the modulation accuracy is lowered
as the reduction in the PAPR increases.

DISCLOSURE OF THE INVENTION

[0008]The TR with RT process is capable of reducing the PAPR without
causing the EVM to increase (modulation accuracy to decrease). In the TR
with RT process, however, the maximum reduction in the PAPR is limited by
the number of subcarriers.

[0009]In the TR without RT process, the maximum reduction in the PAPR is
not limited by the number of subcarriers. However, the EVM becomes higher
as the reduction in the PAPR is increased in the TR without RT process.

[0010]Insofar as a target PAPR can be achieved by the TR with RT process,
the PAPR can be lowered by the TR with RT process without highering the
EVM at all. Insofar as a target PAPR cannot be achieved by the TR with RT
process, it is necessary to use the TR without RT process for achieving
the target PAPR. However, the TR without RT process tends to higher the
EVM as the PAPR is lowered. If the EVM that is required is lower than a
value at the time the target PAPR is achieved by the TR without RT
process, then the TR without RT process cannot be used.

[0011]As described above, the TR with RT process and the TR without RT
process have both advantages and disadvantages. Neither of them is able
to perform a peak reduction sequence for satisfying both a target signal
power peak reduction and a required modulation accuracy.

[0012]It is an object of the present invention to provide a transmission
signal generating apparatus which is capable of achieving both a
modulation accuracy and a signal power peak reduction in a balanced
manner.

[0013]To accomplish the above object, according to an aspect of the
present invention, a transmission signal generating apparatus for
generating transmission signals with reduced peak power, comprises:

[0014]data multiplexing subcarrier identification signal generating means
for generating a data multiplexing subcarrier identification signal that
identifies subcarriers with which data signals are to be multiplexed;

[0016]peak reducing transmission signal generating means for generating
peak reducing transmission signals by reducing peak power of said
transmission signals generated by said transmission signal generating
means according to peak reducing signals in a combination of a first peak
reducing process in which subcarriers with which the data signals are not
multiplexed are used for the peak reducing signals and subcarriers with
which the data signals are multiplexed are not used for the peak reducing
signals based on said data multiplexing subcarrier identification signal,
and a second peak reducing process in which both subcarriers with which
the data signals are not multiplexed and the subcarriers with which the
data signals are multiplexed are used for the peak reducing signals.

[0017]According to an aspect of the present invention, a transmission
signal generating method of generating transmission signals with reduced
peak power comprises:

[0018]generating a data multiplexing subcarrier identification signal that
identifies subcarriers with which data signals are to be multiplexed;

[0019]generating transmission signals by multiplexing data signals with
subcarriers according to the data multiplexing subcarrier identification
signal; and

[0020]generating peak reducing transmission signals by reducing peak power
of said transmission signals according to peak reducing signals in a
combination of a first peak reducing process in which subcarriers with
which the data signals are not multiplexed are used for the peak reducing
signals and subcarriers with which the data signals are multiplexed are
not used for the peak reducing signals based on said data multiplexing
subcarrier identification signal, and a second peak reducing process in
which both subcarriers with which the data sipals are not multiplexed and
the subcarriers with which the data signals are multiplexed are:used for
the peak reducing signals.

[0021]According to an aspect of the present invention, a transmission
signal generating program for controlling a transmission signal
generating apparatus to generate transmission signals with reduced peak
power, comprises:

[0022]a sequence to generate a data multiplexing subcarrier identification
signal that identifies subcarriers with which data signals are to be
multiplexed;

[0023]a sequence to generate transmission signals by multiplexing
data.signals with subcarriers according to the data multiplexing
subcarrier identification signal; and

[0024]a sequence to generate peak reducing transmission signals by
reducing peak power of said transmission signals according to peak
reducing signals in a combination of a first peak reducing process in
which subcarriers with which the data signals are not multiplexed are
used for the peak reducing signals and subcarriers with which the data
signals are multiplexed are not used for the peak reducing signals based
on said data multiplexing subcarrier identification signal, and a second
peak reducing process in which both subcarriers with which the data
signals are not multiplexed and the subcarriers with which the data
signals are multiplexed are used for the peak reducing signals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a block diagram showing a configuration of a transmission
signal generating apparatus according to a first exemplary embodiment;

[0026]FIG. 2 is a block diagram showing a configuration of a transmission
signal generator according to the first exemplary embodiment;

[0027]FIG. 3 is a block diagram showing a configuration of a peak reducing
signal generator according to the first exemplary embodiment;

[0028]FIG. 4 is a diagram showing the generation of a peak reducing pulse
signal with a data orthogonal peak reducing pulse generator according to
the first exemplary embodiment;

[0029]FIG. 5 is a diagram showing the generation of a peak reducing pulse
signal with a data common peak reducing pulse generator according to the
first exemplary embodiment;

[0030]FIG. 6 is a graph showing the results of a simulation with respect
to the first exemplary embodiment;

[0031]FIG. 7 is a table showing evaluated values of PAPR reduction and
modulation accuracy with respect to the first exemplary embodiment;

[0032]FIG. 8 is a block diagram showing a configuration of a peak reducing
signal generator according to a second exemplary embodiment;

[0033]FIG. 9 is a diagram showing the generation of peak reducing pulse
signals with a data common peak reducing pulse generator according to a
third exemplary embodiment;

[0034]FIG. 10 is a block diagram showing a configuration of a transmitter
according to a fourth exemplary embodiment;

[0035]FIG. 11 is a table showing evaluated values of PAPR reduction gain
with respect to the fourth exemplary embodiment; and

[0036]FIG. 12 is a graph showing throughputs vs. SIRPre.

BEST MODE FOR CARRYING OUT THE INVENTION

[0037]Exemplary embodiments of the present invention will be described in
detail with reference to the drawings.

[0048]Peak reducing transmission signal generator 102 is a block for
repeating a peak reducing transmission signal generating process a given
number of times on prior-to-peak-reduction signals SPreTx(1),
SPreTx(2), . . . , SPreTx(S) from transmission signal generator
101. Specifically, peak reducing transmission signal generator 102
performs a peak reducing transmission signal generating process based on
TR with RT a given number of times (E times), and then performs a peak
reducing transmission signal generating process based on TR without RT a
given number of times (F times) where E and F are natural numbers.

[0051]Data common peak reducing pulse generator 303 which is supplied with
data multiplexing subcarrier identification signal SDM generates
data common peak reducing pulse signals SDCPL(1), SDCPL(2), . .
. , SDCPL(R), and outputs them to peak reducing pulse selector 304.
At this time, as shown in FIG. 5, data common peak reducing pulse
generator 303 sets the components of a total of Q subcarriers, i.e.,
subcarriers which do not correspond to data multiplexing subcarrier
identification signal SDM and subcarriers which correspond to data
multiplexing subcarrier identification signal SDM, to 1 and sets the
components of a total of (R-Q) subcarriers at high frequencies and low
frequencies to 0, thereby setting a total of R subcarriers. FIG. 5 shows
by way of example subcarriers for use with data common peak reducing
pulse signals based on TR without RT. Data common peak reducing pulse
generator 303 performs IFFT with R points on the R subcarriers, thereby
generating data common peak reducing pulse signals SDCPL(1),
SDCPL(2), . . . , SDCPL(R).

[0058]At this time, peak reducing signal calculator 305 first detects peak
signal points SPeak(i,1), SPeak(i,1), . . . ,
SPeak(i,U(i)) whose signal power exceeds a given threshold A from
ith prior-to-peak-reduction transmission signals S.sub.PPre(i,1),
S.sub.PPre(i,2), . . . , S.sub.PPre(i,S), where A represents a positive
real number and U(i) represents a natural number equal to or smaller than
S.

[0059]Then, peak reducing signal calculator 305 multiplies peak reducing
pulse signals SPPL(1), SPPL(2), . . . , SPPL(R) by the
value of the component exceeding the threshold A with respect to each of
the detected peak signal points SPeak(i,V) (V represents a natural
number equal to or smaller than U(i)). Furthermore, peak reducing signal
calculator 305 shifts the product signals in a negative direction by X
samples so that the absolute values of the amplitudes of the peak
reducing pulse signals will be maximum at a sampling time 0, thereby
generating peak component multiplication signals SMUPK(i,V,1),
SMUPK(i,V,2), . . . , SMUPK(i,V,S) where X represents an
integer equal to or greater than 0 and smaller than S.

[0065]According to the present exemplary embodiment, as described above,
peaks of transmission signals are reduced according to a combination of a
peak reducing process based on TR with RT which is free of
modulation-accuracy reductions, and a peak reducing process based on TR
without RT which does not limit peak reductions depending on the number
of RT subcarriers not used for data signals. Therefore, signal power peak
reductions can be increased while modulation accuracy reductions are
minimized.

[0066]Modulation accuracy reductions caused by the peak reducing process
based on TR without RT depend on the PAPR reduction. According to the
present exemplary embodiment, the peak reducing process based on TR with
RT is carried out, and then the peak reducing process based on TR without
RT is carried out. Therefore, peaks of transmission signals are reduced
by the peak reducing process based on TR with RT prior to the peak
reducing process based on TR without RT, thereby reducing modulation
accuracy reductions which tend to be caused when a target signal power
peak reduction is achieved.

[0067]The results of an evaluation of the first exemplary embodiment will
be described below.

[0068]FIG. 6 is a graph showing the results of a simulation with respect
to the first exemplary embodiment. FIG. 6 illustrates a complementary
cumulative distribution function (CCDF) representing a peak-to-average
power ratio.

[0069]According to the present simulation, both E and F are set to 1.
Specifically, the peak reducing process based on TR with RT using a data
orthogonal peak reducing pulse signal is performed once, and then the
peak reducing process based on TR without RT using a data common peak
reducing pulse signal is performed once.

[0070]FIG. 7 is a table showing evaluated values of PAPR reduction and
modulation accuracy with respect to the first exemplary embodiment. FIG.
7 illustrates, for comparison with the present exemplary embodiment,
evaluated values obtained when only the peak reducing process based on TR
with RT is performed and evaluated values obtained when only the peak
reducing process based on TR without RT is performed, as well as the
evaluated values according to the present exemplary embodiment.

[0071]As shown in FIG. 7, according to the peak reducing process based on
TR without RT, EVM is 3.1% when a PAPR reduction of 1.4 dB (@CCDF=99.9%)
is achieved. A maximum PAPR reduction obtained by the peak reducing
process based on TR with RT is 1.2 dB.

[0072]According to the present exemplary embodiment, EVM is 1.0% when a
PAPR reduction (1.5 dB) comparable to a PAPR reduction (1.4 dB) obtained
by the peak reducing process based on TR without RT is achieved.
According to the present exemplary embodiment, therefore, the modulation
accuracy is improved by 2.1%.

[0073]According to the present exemplary embodiment, furthermore, while
the spectrum use efficiency remains comparable to that of the peak
reducing process based on TR with RT, the peak reduction is 0.3 dB better
than the maximum PAPR reduction according to the peak reducing process
based on TR with RT.

Second Exemplary Embodiment

[0074]According to the first exemplary embodiment, the number of times (E
times) that the peak reducing process based on TR with RT is carried out
and the number of times (F times) that the peak reducing process based on
TR without RT is carried out are predetermined. According to the second
exemplary embodiment, the peak reducing process based on TR with RT is
switched to the peak reducing process based on TR without RT and the peak
reducing process based on TR without RT is finished based on comparison
of signal powers with a threshold value.

[0079]According to the present exemplary embodiment, as described above,
since the peak reducing process based on TR without RT is finished based
on comparison of signal powers with a threshold value, the peak reducing
process is finished when a target peak reduction is reached, and hence a
target signal power peak reduced can be reached with a higher modulation
accuracy.

[0080]According to the present exemplary embodiment, moreover, the peak
reducing process based on TR with RT is switched to the peak reducing
process based on TR without RT based on comparison of signal powers with
a threshold value. Consequently, the peak reducing process based on TR
without RT can be carried out after peaks are reduced to a certain level
by the peak reducing process based on TR with RT which is free of
modulation accuracy reductions. As a result, modulation accuracy
reductions which increase depending on the PAPR reductions in the peak
reducing process based on TR without RT are minimized.

[0081]In the present exemplary embodiment, in order to prevent a
processing delay of the overall peak reducing transmission signal
generating process from increasing beyond a certaro level as the number
of times thal the peak reducing process is repeated increases, threshold
value determining section 401 may have upper limits predetermined for the
number of times that the peak reducing processes based on TR with RT and
TR without Rt are repeated.

[0082]In such a case, when the number of times that the peak reducing
process based on TR with RT is repeated reaches its upper limit,
threshold value determining section 401 may output peak reducing pulse
switching signal STG to peak reducing pulse selector 304' even
through the signal powers have not been reduced below threshold value G.

[0084]According to the first exemplary embodiment, data common peak
reducing pulse generator 303 generates data common peak reducing pulse
signals SDCPL(1), SDCPL(2), . . . , SDCPL(R) using the
components of all subcarriers with which data symbols not corresponding
to data multiplexing subcarrier identification signal SDM are not
multiplexed and the compoments of all subcarriers with which the data
symbols are multiplexed. According to the third exemplary embodiment,
data common peak reducing pulse generator 303 selects subcarriers used
for data common peak reducing pulse signals from the subcarriers with
which the data symbols are multiplexed, based on a required modulation
accuracy or a modulation multilevel number.

[0085]For maximizing the transmission rate, there is a technology which
determines the modulation multilevel number for each subcarrier with the
reception SNR (signal to noise power ratio) of the subcarrier in a
wireless terminal. According to the technology, a different modulation
accuracy is determined based on the modulation multilevel number in
specifications or the like, and a higher modulation accuracy is required
as the modulation multilevel number is greater.

[0086]When data symbols with different modulation multilevel numbers are
multiplexed in an entire signal band, if the modulation accuracy after
peaks of all subcarriers have been reduced is limited to match the
modulation accuracy required by data symbols with the greatest modulation
multilevel number, then a sufficient peak reduction may not be achieved
because the modulation accuracy may unnecessarily be limited.

[0087]According to the present exemplary embodiment, subcarriers for which
a modulation accuracy equal to or higher than a certain level is required
are not used for data common peak reducing pulse signals. Specifically,
data common peak reducing pulse generator 303 according to the present
exemplary embodiment sets the components of subcarriers, among all the
subcarriers with which data symbols are multiplexed, for which a
modulation accuracy equal to or higher than a certain level is required
to 0 and also sets the components of remaining subcarriers to 1, thereby
generating data common peak reducing pulse signals. In this manner, high
peak reductions can be achieved while reductions in the modulation
accuracy for data symbols with large modulation level numbers are
lowered.

[0088]FIG. 9 is a diagram showing the generation of peak reducing pulse
signals with a data common peak reducing pulse generator according to the
third exemplary embodiment. In the example shown in FIG. 9, modulation
processes QPSK and 64 QAM having different modulation level numbers for
data symbols are used. The modulation process 64 QAM with a larger
modulation level number is required to have a higher modulation accuracy
than the modulation process QPSK with a smaller modulation level number.

[0089]According to this example, only subcarriers with which data symbols
of QPSK with a smaller modulation level number are used for peak reducing
signals, and subcarriers with which data symbols of 64 QAM with a larger
modulation level number are multiplexed are not used for peak reducing
signals. Consequently, peak powers can be reduced without lowering the
modulation accuracy of the data symbols of 64 QAM.

Fourth Exemplary Embodiment

[0090]According to a fourth exemplary embodiment, the functions about the
peak reduction process according to the first exemplary embodiment
described above are set out in greater detail. FIG. 10 is a block diagram
showing a configuration of a transmitter according to the fourth
exemplary embodiment.

[0091]The transmitter according to the fourth exemplary embodiment
corresponds to the transmission signal generating apparatus according to
the first exemplary embodiment. The transmitter and a receiver (not
shown) for receiving wireless signals transmitted from the transmitter
jointly make up a wireless transmission system. It is assumed that the
receiver measures an SIR (signal to interference power ratio) value of
signals received from the transmitter, and feeds the measured SIR value
back to the transmitter.

[0092]According to the present exemplary embodiment, a stage for carrying
out the peak reducing process based on TR with RT is referred to as a
first stage, and a stage for carrying out the peak reducing process based
on TR without RT is referred to as a second stage. As shown in FIG. 10,
transmitter 500 comprises peak reducing parameter generator 501, data
generator 502, data multiplexer 503, peak reducing subcarrier generator
504, peak detector 505, FIR (Finite Impulse Response) section 506, delay
section 507, subtractor 508, IFFT sections 2041 through 2043,
and repetition selector 301.

[0093]Peak reducing parameter generator 501 calculates SIR(SIRPre) in
the receiver at the time a PAPR reducing process is not applied, by
giving SIR information (SIRPost) fed back from the receiver and
improved amount (V) of transmission power at the time a preceding PAPR
reducing process is performed, to an equation (1) below. The time when
the preceding PAPR reducing process is performed refers to the time when
the PAPR reducing process is performed in a preceding cycle, which is one
feedback RTT (Round Trip Time) earlier.

[0095]Peak reducing parameter generator 501 holds an association table
which is representative of SAL, STWRT, STWORT for
maximizing the throughput for each SPre, and uses the association
table for generating SAL, STWRT, STWORT based on
SIRPre.

[0096]Improved amount (V) of transmission power is determined by giving,
to an equation (2) below, PAPR at the time the PAPR reducing process is
not applied (R in the equation (2)), STWORT at the time the
preceding PAPR reducing process is applied (one RTT earlier), the power
of peak reducing signals (b in the equation (2), and a BLER reduction due
to the PAPR reducing process (c in the equation (2).

[0113]According to the present exemplary embodiment, as described above,
the peak reducing process based on TR with RT which is modulation
accuracy reductions and the peak reducing process based on TR without RT
which does not limit peak reductions depending on the number of RT
subcarriers not used for data signals are combined with each other to
reduce peaks of transmission signals. Consequently, signal power peak
reductions can be increased while modulation accuracy reductions are
minimized.

[0114]Modulation accuracy reductions caused by the peak reducing process
based on TR without RT depend on the PAPR reduction. According to the
present exemplary embodiment, the peak reducing process based on TR with
RT is carried out, and then the peak reducing process based on TR without
RT is carried out. Therefore, peaks of transmission signals are reduced
by the peak reducing process based on TR with RT prior to the peak
reducing process based on TR without RT, thereby reducing modulation
accuracy reductions which tend to be caused when a target signal power
peak reduction is achieved.

[0115]The results of an evaluation of the fourth exemplary embodiment will
be described below.

[0116]Improved amount (V) of transmission power is defined as a PAPR
reduction gain. An allowable amount for an EVM reduction due to the PAPR
reduction is set to 3% at maximum. Since a BLER (block error rate)
measured in the receiver due to an EVM reduction is smaller than 0.1 dB,
c in the equation (2) is assumed to be 0.

[0117]The subcarrier number (N) is set to 300, and QPSK, 16 QAM
modulation, and a turbocode (R=1/3, 1/2, 2/3, 3/4, 4/5) are used for the
evaluation. A propagation path for evaluating the BLER is Typical Urban 6
path, with the Doppler frequency being of 5.55 Hz.

[0119]FIG. 11 is a table showing evaluated values of PAPR reduction gain
with respect to the fourth exemplary embodiment. The table shows that
according to the fourth exemplary embodiment, the PAPR reduction gain is
improved by about 1.3 dB based on TR with RT and about 0.8 dB through 1.8
dB based on TR without RT.

[0120]FIG. 12 is a graph showing throughputs vs. SIRPre.

[0121]According to the fourth exemplary embodiment, higher throughputs are
realized than when the peak reducing process based on TR with RT and the
peak reducing process based on TR without RT according to the background
art are carried, not based on SIRPre. Particularly, in a low SIR
range which is short of transmission power, the throughputs are highly
improved according to the fourth exemplary embodiment. When SIRPre
is -5 dB (SAL=0.2, STWORT=6.4 dB, STWORT=5.0 dB), a
throughput which is about 2.4 times the throughput based on TR without RT
and a throughput which is about 2.0 times the throughput based on TR with
RT are achieved according to the fourth exemplary embodiment.

[0122]The present invention has been described above in reference to the
exemplary embodiments thereof. However, the present invention is not
limited to the exemplary embodiments. Various changes that can be
understood by those skilled in the art can be made in the configurations
and details of the present invention, which are defined in the claims,
within the scope of the present invention.

[0123]The present application claims priority based on Japanese patent
application No. 2007-172127 filed on Jun. 29, 2007, and incorporates
herein the disclosure thereof in its entirety by reference.